BOSTON — Incumbent Democratic Gov. Deval Patrick was the lone candidate to defend a planned wind farm off Cape Cod at a gubernatorial debate Monday focused on the future of renewable energy in Massachusetts.

Patrick said the proposed 130-turbine Cape Wind project in Nantucket Sound will thrust the state to the forefront of offshore wind energy in the US and guarantee reliably priced electricity into the future.

"Offshore wind, wave and tidal are our biggest opportunities for locally generated clean energy," Patrick said. "I think it's an important symbol for us to be a leader."

He also said nation's first offshore wind farm will also create up to 1,000 jobs and help make Massachusetts a hub for a new energy industry.

Baker faulted the project for not being competitively bid and said it will result in higher electricity costs and automatic price increases for homeowners and businesses, making it harder for the state to lure sorely needed jobs.

He said the project is also receiving subsidies that could be better spent elsewhere.

"There are other alternatives that are available to us that are cheaper, more affordable and in the end, I believe, better from a diversification strategy," he said. "This is a monstrous big bet on one project."

Cahill echoed those concerns, faulting a power purchasing deal that enables annual percentage increases in the energy purchased from the wind farm. He also accused the Patrick administration of trying to pick winners and losers instead of letting the market decide.

"It's not going to work for Massachusetts," Cahill said. "Cape Wind is the wrong project in the wrong place at the wrong time."

At the heart of Baker's and Cahill's criticism was a deal approved last month by Attorney General Martha Coakley's office.

Under that deal, Coakley recommended state regulators approve a power purchasing deal between Cape Wind and utility National Grid that would set its starting price for electricity at 18.7 cents per kilowatt hour in 2013. The price would be allowed to rise 3.5 percent annually.

The deal must still be approved by state utility regulators.

The cost of the project also drew the criticism of Green Rainbow candidate Jill Stein, who said Cape Wind was too expensive and the state should focus on encouraging other renewable sources or energy and making existing homes and businesses more energy efficient.

"We need to get the most green energy from each dollar that we invest," Stein said. "As Cape Wind comes to us today it is clearly not delivering the most green energy for each dollar invested."

Cape Wind has been at the center of a battle stretching back nearly a decade as community groups and top political figures, including the late Sen. Edward Kennedy, fought against it.

The project has survived legal challenges and regulatory hurdles. In April it received the approval of U.S. Interior Secretary Ken Salazar.

Although the debate, sponsored by the public policy think tank MassINC and Suffolk University, focused on renewable sources of energy like wind power, the candidates were also asked about other forms of power, including nuclear.

Cahill was the most vocal, calling the new generation of nuclear plants safer and cleaner than earlier versions.

Patrick said he likes "everything about nuclear" except for the problem of disposing of nuclear waste, while Baker said the nuclear plants should continue to be a part of the state's energy portfolio.

Stein called renewed talk of nuclear power "incredibly foolhardy."

The candidates also staked out different opinions on the question of global warming.

While all four said they agreed that the globe is warming, Cahill and Baker said that warming was only partially attributable to human activity.

Patrick said the warming was "mostly" attributable to people while Stein said that "virtually all" of it was humans' fault.

Patrick has made renewable energy a hallmark of his first term and earlier this month won the endorsement of environmental groups including Massachusetts Clean Water Action, the Massachusetts League of Environmental Voters, and the Massachusetts Chapter of the Sierra Club.

But critics have also said Patrick hasn't always been able to hold onto new green jobs.

During the debate Cahill pointed to Marlborough-based Evergreen Solar Inc. which has received $58 million in state aid but last year announced it was planning to move some jobs to China.

Patrick said the company has already created more than the promised numbers of jobs in Massachusetts and so far no jobs have been shipped to China.

On the question of what car they drive, Cahill said a Jeep Laredo, Baker said a Chrysler 300 and Stein said a Prius Hybrid.

Patrick said he owns a Mercedes convertible, which he called a "midlife crisis" car he hasn't been able to use since becoming governor because he is driven in a state owned Tahoe Hybrid.